The present invention relates generally to conductive medical leads including fixation electrodes. More particularly, this invention is directed to aspects related to maintaining more reliable electrical conductive contact in implantable fixation lead electrodes and urging such electrodes to remain in an extended, implanted position.
Implantable leads form an electrical connection between a pulse generator or other electronic device and a tissue or structure in the body. For example, leads transmit electric signals used to stimulate cardiac or nerve tissue in one direction and signals generated by sensors placed in proximity to particular organs or tissues in the opposite direction. Cardiac leads are normally passed through the veins of a patient to form an electrical connection between a pulse generator or other electronic device and the heart.
Medical leads typically include one or more electrodes or sensors at the distal end of the lead. The electrodes are designed to form an electrical connection with a tissue or organ. A flexible conductor electrically connects the electrode to the pulse generator. The electrodes may be passively or actively attached to a target location within the patient. Passive fixation typically employs tines to interlock with the target tissue. Active fixation frequently utilizes a screw helix or similar structure to bore into the tissue to secure the lead. To allow the introduction of the lead to occur benignly without damaging tissue, the screw helix is typically retracted and maintained within a cavity in the electrode housing during insertion. The screw helix may function solely as an anchoring device or may additionally function as an electrode or sensor. When the screw helix functions as an electrode or a sensor, a need exists to maintain the integrity of the electrical connection between the helix and the conductors within the lead body.
Forming a secure electrical junction between the conductors and a screw helix has proven difficult and time consuming. Because of the need to rotate the helix during implantation, a rotatable connection must be formed within the electrode. Related devices have used the contact inherent in a threaded relationship between the piston base of the screw helix and the electrode housing to provide the necessary electrical connection. Thus, the threaded relationship of related art functioned to both advance the screw helix and provide an electrical connection between the screw helix and the conductors. The threaded elements may suffer from transient loss of the electrical contact between the base and the conductors due to the play necessary to allow relative rotation. The beating of the heart may further exacerbate this problem. That is, as the heart beats, the tip electrode is subjected to frequent forces which may result in transient electrical isolation of the screw helix. In application, the transient isolation can provide gaps or spikes in sensed data and interfere with the transmission of pacing stimuli. Therefore, a need exists for a more reliable rotatable connection that provides uninterrupted contact between the electrode and the screw helix.
In addition, the movement of the heart, in time, can cause the extended helix anchor that penetrates the tissue to rotate and retract or withdraw into the electrical assembly. Therefore, a need also exists for an electrode assembly that reliably maintains the helix in an extended orientation after implantation.
The present invention meets the above-described needs and provides additional advantages and improvements that will be evident to those skilled in the art upon further review of the disclosure.
By means of the present invention, many of the problems associated with prior leads are solved by the provision of an implantable medical lead of superior electrical contact security which, in addition, inhibits unwanted withdrawal of implanted electrode anchors. The present invention provides a secure uninterrupted electrical connection between a screw helix and a conductor.
The medical lead of the invention includes a medical electrode connected to the distal portion of the lead for use to electrically stimulate selected body tissues or to transmit signals from a sensor to a medical device. One illustrative or detailed embodiment of the invention generally involves a hot or conductive helical anchor electrode lead or fixation electrode for a cardiac pacing lead. The device includes an electrode base attached to the distal portion of the elongated lead body. A generally hollow electrode housing which defines an internal cavity is connected to the electrode base through the proximal end of the housing. A distal portion of the internal surface of the electrode housing is provided with helical threads. A piston member having matching external threads is rotatably mounted within the housing cavity and the internal housing threads to thereby move along said housing upon rotation relative thereto. A screw helix electrode-carrying anchor including a sharp distal tine is attached to the piston so as to rotate along with it. The piston and the screw helix electrode and anchor or fixation mechanism are of electrically conducting materials and a resilient conductor member is mounted between the piston and the electrode base to electrically connect the piston with the electrode base so that a positive electrical connection exists between the electrode anchor and the electrode base even when the piston is fully extended.
The electrical housing also may or may not be of a conductive material, depending on the nature of the application. In the case of conductive housings, the resilient conductor member may secure continuous conduction between the piston and the housing.
The resilient conductor member which electrically connects the piston and the electrode base or housing, not only provides a superior uninterrupted electrical contact, but also aids in preventing retraction of the piston once the electrode/anchor is in place in the heart muscle of the patient or other location by urging the piston to remain extended. Whereas other shapes and materials are contemplated, metal compression spring clips and memory-shaped or contact washers have been found useful.
Thus, it can be seen that the present invention provides a secure electrical connection between a screw helix electrode and anchor and a remote conductor in the manner which also aids in maintaining the position of an implanted electrode/anchor of the screw helix class. Other embodiments may occur to those skilled in the art upon familiarization with the contents of the specification.